Big on the Inside

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Appearances can be deceiving, especially so when it comes to the South American lungfish.

This freshwater creature can grow to four feet in length. But its genome is the largest ever sequenced in a creature, a new study has found.

A research team studying the lungfish species – scientifically known as Lepidosiren paradoxa – discovered that it had a whopping 91 billion base pairs.

That’s around 30 times bigger than the human genome.

The DNA of the South American species “is the largest of all animal genomes and more than twice as large as the genome of the previous record holder, the Australian lungfish,” claimed lead author Axel Mayer in a press release. “(Eighteen) of the 19 chromosomes of the South American lungfish are each individually larger than the entire human genome with its almost 3 billion bases.”

Meyer and his colleagues explained that these copious amounts of genes are mainly “junk DNA” that don’t serve any particular purpose. They noted that this massive genome is largely attributed to the presence of autonomous transposons, also known as “jumping genes.” These sequences can copy themselves and move around within the genome, leading to rapid expansion.

Humans also have jumping genes, but we have some mechanisms to control them. That’s not the case with the L. paradoxa, whose genome grows at an extraordinary rate, adding a sequence equivalent to the entire human genome approximately every 10 million years, Smithsonian Magazine noted.

Still, this ever-growing genome is stable and proves advantageous for the creature, allowing it to quickly adapt to changing environments and drive the evolution of new genes.

Lungfish are considered the closest living relatives of tetrapods – the first four-legged creatures that moved from water to land around the epoch of the Devonian Period, 419 to 359 million years ago.

By studying the lungfish genome, scientists have gained insights into how these early vertebrates evolved limbs from fins, a crucial step in the transition from aquatic to terrestrial life.

The findings can help reconstruct the genomic and evolutionary journey from fish to tetrapods, as well as offer a glimpse into the latter’s original chromosomal architecture, added Popular Mechanics.